Reply To: When to use tongue and groove?
Hej Waldo,
If I understand Prof. R. Bruce Hoadley’s “Understanding Wood” correctly, splines / tongue-grooves actually weaken edge joints. The tongues were clearly the least strong parts when I laid out 1¾” thick floor boards at our croft. The tongues were 3/8″ thick, but they did not contribute in keeping the boards flat.
Loose tenons, and possibly biscuits, apparently do add strengths, as has been shown for the Festool Domino System; but neither have contributed to make my table tops and panels easier to glue up or kept them flatter. Admittedly, my clumsiness reaches its peak when it’s time for glueing.
Please accept a link to the Wood Database. With the modulus of rupture given for maple, it seems unlikely that a 30 mm thick table top will bow from gravity.